An ozone generator is an apparatus capable of flowing an oxygen-containing gas such as air in a thermal non-equilibrium plasma to produce ozone. The thermal non-equilibrium plasma is generated utilizing a discharge provided by a discharge generating device. For example, the discharge generating device may be of a silent discharge type. In this type of device, for example, a high voltage of several to several tens kV is applied by a high-voltage alternating-current power source to a discharge gap between a high-voltage electrode and a ground electrode, to generate a discharge of an aggregate of micro-discharge columns. The oxygen-containing gas is decomposed in the discharge process to produce ozone.
Conventional structures of such ozone generators are disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 10-324504, and 2013-193893.
Japanese Laid-Open Patent Publication No. 10-324504 discloses in paragraph [0002] that “A silent discharge-type ozone generator has electrodes facing each other and one or two dielectric bodies interposed between the electrodes. A high alternating-current voltage is applied to the electrodes while flowing an oxygen-containing source gas (such as a high-concentration oxygen (PSA oxygen) gas or a dehumidified air) in a gap between the electrode and the dielectric body or between the dielectric bodies, and oxygen is dissociated by a silent discharge to produce ozone. The gap has a length of about 1 mm, and the dielectric body is composed of a glass or ceramic material having a high dielectric strength”.
Further, Japanese Laid-Open Patent Publication No. 10-324504 discloses in paragraph [0015] that “The ozone generator 2 includes a hard glass tube (dielectric body) 9 having an outer diameter of 18 mm and a thickness of 0.9 mm, a film electrode 10 adhered to an outer surface of the glass tube 9, and a spiral electrode (made of SUS316 and having a diameter of 0.5 mm) 11 adhered to an inner surface thereof”. The Publication also discloses in paragraph [0015] that “in the ozone generator 2, a dehumidified air or a high-concentration oxygen (PSA oxygen, having the oxygen concentration of 95% or more) is supplied as a source gas from one end of the glass tube 9, a high alternating-current voltage (several to some dozen kV, 40 kHz) having the switching frequency of 0.1 to 1000 cycles per second and the load factor of 5 to 95% is applied, and then ozone air (air containing ozone) is discharged from the other end of the glass tube 9”. Further, the Publication discloses in paragraph [0020] that “in a case of the flow rate of dehumidified air of 1.0 L/min”. Also, the Publication discloses in paragraph [0005] that “the gap between the dielectric body and the electrode or the gap between the dielectric bodies is further narrowed (to 0.5 to 1 mm)”.
Japanese Laid-Open Patent Publication No. 2013-193893 discloses in paragraph [0011] that “an ozone generator contains a cylindrical high-voltage electrode, a cylindrical low-voltage electrode arranged coaxially with the high-voltage electrode, and a dielectric body between the electrodes. A dry air is supplied as a source gas between the electrodes, and a predetermined high voltage is applied through the dielectric body between the high-voltage and low-voltage electrodes to generate a discharge, whereby ozone is produced by the discharge. The discharge gap length d is 0.3 to 0.5 mm”. Further, the Publication discloses in paragraph [0018] that “In addition, a pd product, which is a product of the discharge gap length d and a gas pressure p of the raw material gas (air), is in a range of 6 to 16 kPa·cm. Further, in the present embodiment, the discharge gap length d (cm) and the gas pressure p of the raw material gas (kPa) are set to satisfy the following expression”.
Japanese Laid-Open Patent Publication No. 10-324504 discloses that, in the creeping discharge type ozone generator, the alternating-current voltage having the discharge frequency of 40 kHz is applied in the cylindrical tube having the outer diameter of 18 mm and the thickness of 0.9 mm, and the dehumidified air is supplied at the flow rate of 1.0 L/min. However, the Publication does not disclose what the flow velocity of the source gas in the discharge space should be in order to reduce the decomposition of ozone.
Japanese Laid-Open Patent Publication No. 2013-193893 explains the ozone production efficiency in relation to the discharge gap length and the source gas pressure. However, the gas pressure can be arbitrarily changed depending on the tube length and the air amount.
Further, the technology disclosed in Japanese Laid-Open Patent Publication No. 2013-193893 is effective in a case of a coaxial cylindrical ozone generator in which all the supplied source gas flows through the discharge space. However, the technology is not effective in a case of an ozone generator that includes electrodes arranged at a predetermined distance, each electrode having a cylindrical ceramic dielectric body and a conductive body disposed in the ceramic dielectric body. This is because the source gas also flows through spaces other than the discharge space, so that the source gas pressure varies depending on the volume of the spaces other than the discharge space.